Update building-setup-windows-cygwin.rst

[chenyuanzhen]

cygwin waf use /usr/bin/python3 not /usr/bin/python

[TunaLobster]

Not bad idea. I haven't had issues with this though. These commands are different/non-existent in the environment setup script. Was there a reason to deviate from what was in the install script? https://github.com/ArduPilot/ardupilot/blob/master/Tools/environment_install/install-prereqs-windows.ps1

[khancyr]

we should probably nuke the whole instruction and ask to use the script, that would be one less diff to maintain.

otherwise the change look good as we are now correctly supporting python3 .

[Hwurzburg]

@TunaLobster @khancyr need someone to approve before I can merge this

[chenyuanzhen]

The system I was using at the time was windows11, and I did use Tools/environment_install/install-prereqs-windows.ps1 for installation. There were no errors during the installation. But when executing the ln -s /usr/bin/python3.7 /usr/bin/pythoncommand, the terminal prompts that the creation failed and /use/bin/python already exists. However, this may be because python2 was already installed on the computer before running install-prereqs-windows.ps1 . As a result, when running the ./waf command, python2 is used, and ultimately fails because all dependencies are installed in python3.
Finally i use ln -sf /usr/bin/python3.7 /usr/bin/python3 command, waf use correct version of python, and all things run ok.